The invention relates to a diaphragm pump, particularly for dosing or metering liquids with a diaphragm defining a dosing chamber with a suction and pressure valve on one side and a hydraulic working chamber with drive piston and pressure relief valve on the other.
Diaphragm pumps of this type, which are also known as piston diaphragm pumps, are known in various different constructional forms. The operating principle thereof is that the elastically deformable diaphragm performs its stroke in the working chamber under varying hydraulic pressure in which during the suction stroke in which it enlarges the dosing chamber, it sucks in the liquid to be delivered by means of the suction valve and during the pressure stroke during which it moves into the dosing chamber forces the same out by means of the pressure valve. The pressure change in the working chamber is produced by a piston which closes the same and which is operated by an oscillating drive, e.g. a cam.
Since as a result of the elasticity required of it and the necessary working stroke, the diaphragm has a comparatively limited wall thickness, it is sensitive to overstressing. Such an overstressing can e.g. occur in the case of an excessive suction lift or in the case of a closed or blocked suction line, but also with leaks in the suction or pressure valve. It leads to the diaphragm becoming overstretched and is optionally permanently deformed and in the extreme case even tears. Thus, not only does the diaphragm pump stop operating, but it is also possible for mixing of hydraulic working medium and dosing medium to take place, which leads to corresponding damage.
To avoid excessive deflection of the diaphragm and the resulting risks, separate support means are provided, which limit the diaphragm stroke. These support means generally comprise cup-shaped disks, which are provided with a plurality of channels so that, as a function of the arrangement of the support means, the passage of the working or dosing medium is possible. In the case of a maximum stroke, the diaphragm engages on the cup. Here again damage can occur, in that in the case of an excessively high pressure difference, the diaphragm can be deformed into the channels, so that there are once again permanent deformations or even cracks.